1. Field of the Invention
The present invention relates generally to a reflective mirror having a cooling unit attached thereto. More particularly, the present invention relates to a reflective mirror having a cooling unit attached thereto wherein the reflective mirror is preferably employable in an exposing equipment in which a printed circuit board or the like is exposed to a light beam for the purpose of photochemical treatment.
2. Description of the Prior Art
To facilitate understanding of the present invention, a typical conventional reflective mirror having a cooling unit attached thereto will be described below with reference to FIG. 4 and FIG. 5.
FIG. 4 is a fragmentary sectional view of the conventional reflective mirror having a cooling unit attached thereto, particularly showing a left half of the reflective mirror which is arranged in an exposing equipment for photochemically treating a printed circuit board or the like. A mercury-vapor lamp 2 for emitting ultraviolet rays is arranged as a light source in the spaced relationship relative to a left half of the reflective mirror 20A. A support member 14 of a cast aluminum including a plurality of heat radiating fins 15 is fixedly placed over the rear surface of a reflective plate 17A. A cooling tube 16 of a rubber arranged in the zigzag manner is firmly held between the adjacent heat radiating fins 15 in the clamped state, and each heat radiating fin 15 is radially projected to form a heat radiating plane. A cooling medium flows through the cooling tube 16 to cool the support member 14 by absorbing heat from the reflective plate 17A. The reflective plate 17A made of an aluminum having a high purity is secured to the support member 14 such that it can readily be replaced with another one, as desired.
With the conventional reflective mirror constructed in the above-described manner, the support member 14 is made at an expensive cost and has a low ability of cooling the reflective mirror 17A, causing a temperature of the reflective plate 17A to be elevated greatly. This leads to the result that a reflective capability of the reflective mirror 20A is degraded within a comparatively short period of time and there arises a necessity for often replacing the reflective mirror 20A with another new one.
When the conventional reflective mirror constructed in the above-described manner is practically used, arrangement is made as schematically illustrated in FIG. 5. Specifically, two mirror halves 20A are coupled to each other to provide a single reflective mirror 20B which in turn is accommodated in a case 27. Since a temperature in the case 27 is elevated as the reflective mirror 20B is practically used, an air is introduced into the interior of the case 27 for the purpose of cooling via the inlet port side 18 and then discharged to the outside via an outlet port 19. With such arrangement of the cooling means as mentioned above, however, it has been found that the conventional reflective mirror has the following drawbacks.
1. Since the support member 14 of the reflective mirror 20A is made of a cast aluminum, casting molds are needed to make support members 14 on the industrial basis. However, each casting mold is fabricated at an expensive cost with many man-hours.
2. Although the reflective plate 17A is cooled to some extent with the aid of the heat radiating fins 15, it has a low cooling ability. For this reason, the reflective plate 17A is unavoidably often replaced with another new one because of oxidation caused at an elevated temperature. However, frequent replacement of the reflective plate with another new one requires many manhours, resulting in the reflective mirror 20B being practically used at an expensive cost.
3. To prevent a temperature in the exposing equipment from being elevated undesirably, a large quantity of air is introduced into the interior of the exposing equipment undesirably together with dust. Fine particles in the dust are adhesively deposited on a film during an exposing operation, causing an image on the film to be damaged or injured. As a result, a number of products are rejected as unacceptable products because of the damage or injure caused by contact with the duct in the air.